When downhole tubulars crack or otherwise need repair, patches or cladding are inserted to the proper depth and expanded into contact over the damaged area. As a result of expansion, the cladding assumes a sealed relation with the surrounding tubular. In other applications a hanger attached to a tubular string is inserted into a larger tubular. Expansion is used to anchor and seal the newly inserted string to the existing string.
Expansion is accomplished by driving a swage through the hanger or cladding. Applied hydraulic pressure from the surface is used to stroke a piston, which, in turn, drives the swage. An anchor assembly initially is energized to hold the hanger in response to applied pressure. Initially, the running tool that delivered the hanger is released when the anchor grabs the hanger to provide support for the hanger as the piston strokes the swage to obtain initial support. Once initial support is accomplished the anchor is released and the stroker for the swage is re-cocked for a repetition of the process until the swage passes through the hanger.
The specification for the tubular being repaired or the tubular in which the hanger is to be attached can vary widely. The condition of that tubular can also affect its internal diameter.
When using a swage that has a fixed dimension care must be taken to properly size it for the anticipated inside diameter where the patch or hanger is to be attached. The problem is that there is uncertainty as to the actual inside diameter after years of service. Additionally, a given swage size may be used for a variety of casing weights of a given size. If the actual diameter is smaller than anticipated, there may not be enough available force in the stroking mechanism for the swage to drive it through. In this case the swage will stall and the expansion cannot be properly completed without time-consuming trips out of the hole and replacement swages. Even worse, the swage could hang up in the hanger if it can't be driven all the way through.
One expensive way around this is to use a variable diameter swage that has the ability to change dimension in response to unexpected inside diameter dimension in the tubular in which the patch or hanger is to be attached. Fixed diameter swages are more economical and, in the past, some efforts have been made when using a fixed swage to compensate for unexpected variation from the planned inside diameter. FIGS. 1 and 2 show a prior technique for compensating for dimensional variations in the casing
Referring to FIG. 1, a fixed diameter swage 10 is disposed inside the hanger or cladding 12 and the entire assembly is in position for expansion inside casing 14. When hanger is mentioned it will be considered to also encompass other downhole structures such as patches or cladding. Hanger 12 has an exterior serrated surface 16 built into it for eventual engagement with the casing 14, as shown in FIG. 2. An inner sleeve 18 made of soft material underlays the serrations 16. The intent is for the swage 10 to go inside sleeve 18. If the inside diameter turns out to be smaller than anticipated, then the swage 10 will deform sleeve 18 by design. This can happen because sleeve 18 is made deliberately soft. The objective is to prevent the swage from stalling when the inside diameter of the casing turns out to be smaller than expected. Using sleeve 18 also helps to give the swage 10 an opportunity to provide sufficient contact force against casing 14 by the serrations 16 when the actual inside diameter turns out to be somewhat larger than expected. Yet the ability to provide flexibility and latitude for the actual inside diameter being smaller or larger than anticipated is limited in this design. The apparatus of the present invention seeks to provide greater latitude for diameter variations in both directions that may be incurred in the field. Additionally, the present invention seeks to improve the grip and provide resistance against release from net forces in opposed directions. One way this is accomplished is to take advantage of the phenomenon of longitudinal dimension change of the hanger under compressive or tensile stress that occurs as force is applied to drive the swage. The slip is articulated for radial extension from longitudinal shrinkage to allow a greater variation of inside diameters in which a proper grip can be maintained and the swage driven through without stalling. These and other advantages of the present invention will be more readily appreciated by those skilled in the art from a review of the description of the preferred embodiment and the claims, which appear below.